The present invention relates to a battery charger for a rechargeable battery.
The FIG. 1 shows the block diagram of the battery charger. The battery charger shown in this Fig. is provided with the transformer 1 to change the voltage of the commercial power supply to a voltage suitable for charging the rechargeable battery 4. The transformer connects the primary side components 2 and the secondary side components 3 then the secondary side components 3 is connected to the rechargeable battery 4. At present, the most commonly used battery charger is provided with a switching power supply. The switching power supply changes the input commercial power voltage to a direct current, and inputs this direct current to the primary side of the transformer 1 by switching at a frequency value of, for example, a few tens of KHz. Because the switching power supply changes to a high frequency value, it anables a light weight and small dimension transformer compared to a commercial power supply transformer. The alternating current with its voltage regulated by the transformer 1, is changed into a direct current by the secondary side and supplied to the rechargeable battery 4.
The battery charger shown in FIG. 1, needs an insulation between the primary side and the secondary side of the transformer. Because the primary side uses the commercial power voltage, the voltage gets higher than the secondary side. Because the secondary side is at the voltage suitable for the charging of the rechargeable battery 4, it is a low voltage. To be able to isolate the primary side and the secondary side of the transformer, the primary side components 2 and the secondary side components 3 are fixed on the printed circuit board separated by for example more than 7 or 8 mm. This structure makes the production of a compact battery charger difficult because the printed circuit board is made larger.
It is possible to insulate the primary side and the secondary side by fixing an insulating plate between the primary side components 2 and the secondary side components 3. But it takes time to fix the insulating plate exactly at the right position of the printed circuit board. Especially because the insulating plate, like electronic components, cannot be fixed by soldering on the printed circuit board. For this reason, it is necessary to use a particular structure to fix it mechanically on the printed circuit board, like the primary side components and the secondary side components, it is not possible to fix it efficiently on the printed circuit board. Therefore the structure adding an insulating plate rises the cost of components and as bad effect lowers the production efficiency.
The present invention has been developed to solve the problems of that kind of weak point. The most important purpose of the present invention is to isolate the primary side components and the secondary side components in an ideal condition, and to anable the production of a charge designed compact as a whole.
Furthermore, the other important purpose of the present invention, is to produce a battery charger that can insulate without fail and fix the transformer without needing to fix a component insulating the primary side components from the secondary side components especially on the printed circuit board.
The above and further objects and features of the invention will more fully be apparent from the following description with accompanying drawings.